Control of an engine-driven generator to address transients of an electrical power grid connected thereto

ABSTRACT

A technique for providing electric power to an electric power utility grid includes driving an electric power alternator coupled to the grid with a spark-ignited or direct injection internal combustion engine; detecting a change in electrical loading of the alternator; in response to the change, adjusting parameters of the engine and/or generator to adjust power provided by the engine. In one further forms of this technique, the adjusting of parameters for the engine includes retarding spark timing and/or interrupting the spark ignition; reducing or retarding direct injection timing or fuel amount and/or interrupting the direct injection; and/or the adjusting of parameters for the generator including increasing the field of the alternator or adding an electrical load.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is continuation-in-part of International PatentApplication Number PCT/US2010/001497 filed May 20, 2010, which claimsthe benefit of U.S. Provisional Patent Application No. 61/216,662 filedMay 20, 2009, each of which is hereby incorporated by reference in itsentirety and for all purposes.

BACKGROUND

The present application relates to electrical power generation, and moreparticularly, but not exclusively to techniques to address electricpower grid disruptions, faults, and load transients.

During electrical grid disruptions the voltage of the grid can fluctuaterapidly. Under certain conditions, it may be desirable to maintain thegrid connection of an engine/generator set (genset) when the gridvoltage drops—designated a Low Voltage Ride-Through (LVRT). During alow-voltage event, the generator can lose synchronization with the griddue to the inability of the engine to respond rapidly to the lower poweroutput demand, with the phase angle deviation overshooting due to thenow too high engine power output. In some cases, generator damage may becaused by a corresponding pole-slipped induced current when the gridvoltage returns and the generator is out of synchronization.

Further, when a load change or momentary electrical fault results in agrid voltage drop, the engine may attempt to compensate by increasingits speed. This increase in speed can result in an unacceptable increasein frequency and/or phase angle deviation of the output voltage. Thissituation is of particular concern in utility paralleled applications.

Moreover, a line fault event can suppress the voltage to zero and thenallow it to return in a period of time that is shorter than aconventional engine and the genset control system can react. Thissituation can result in the generator phase angle being significantlydifferent than the returning utility voltage phase angle, as the gensetcontrol is still reacting to the initial fault, possibly causing damageto the generating equipment. Under certain conditions, a genset with aSpark Ignition (SI) genset engine that mixes fuel and air upstream ofthe cylinder can be particularly vulnerable. While the quantity of fuelprovided can be reduced at the first sign of a load change to amelioratethis result, the fuel charge already in existence can pose a problem.Diesel-fueled genset engines can be similarly vulnerable--even thosediesel engines with direct or port fuel injection may performundesirably during an LVRT event despite the ability to change the fuelcharge without having an earlier formed fuel charge present in theintake.

One attempt to address grid fluctuations involves an increase inrotational inertia of the genset by increasing the size/weight of agenset flywheel and/or another rotating mass of the genset. While thisapproach of increasing rotational inertia may address the problem inpart, typically it is not enough to provide desirable performance.

Thus, there remains a need for further contributions in this area oftechnology.

SUMMARY

One embodiment of the present invention is a unique electric powergeneration technique. Other embodiments include unique methods, systems,devices, and apparatus involving genset operation with respect to a lowvoltage ride-through operation of a unique electric power generationtechnique. Further embodiments, forms, objects, aspects, benefits, andadvantages of the present invention shall become apparent from thefigures and description provided herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an electrical power generation systemincluding a genset with an electric power generator and an internalcombustion engine.

FIG. 2 is a diagrammatic view of yet a further electrical power systemincluding parallel gensets.

FIG. 3 is a schematic diagram including circuitry for addressing anelectric power grid disruption.

FIG. 4 is a graph illustrating the operation of the circuitry of FIG. 3.

FIG. 5 is graph depicting electric power grid fault tolerancerequirements for various countries.

FIG. 6 is a graph depicting certain performance aspects of oneembodiment of the present application relative to the fault tolerancerequirements shown in FIG. 5.

FIG. 7 is a graph depicting certain characteristics of an AC sinusoidalwaveform with respect to time.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the described embodiments, and any further applications of theprinciples of the invention as described herein are contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

One embodiment of the present application includes an electrical powersystem with a genset including an engine and an electric power generatoror alternator. The genset may be coupled to provide electric power to autility power grid. If there is a transient voltage drop on the grid,the system responds in any of a number of ways. For instance, the systemmay respond to a low voltage grid condition by temporarily routingexcessive electric current from the generator through a resistivecircuit. Alternatively or additionally, the system addresses abruptchanges in electrical loading that may be caused by an electrical linefault (such as a power grid voltage drop), by adjusting timing of thegenset engine ignition and/or fueling in response and/or adjusting fieldcontrol of the alternator in response. In the case of a spark-ignitedengine, this timing adjustment may include retarding or inhibiting sparkignition of the genset engine. In the case of a fuel-injected dieselengine, whether of the direct injection or port injection type, thistiming adjustment may include reducing the amount of fuel injected,retarding fuel injection and/or inhibiting fuel injection. In one forminvolving the latter, alternator field voltage is increased or evenmaximized (sometimes designated “full field”) to correspondingly raisealternator current to increase the effective load and more closelybalance the engine torque and alternator torque in response to the powergrid voltage reduction. It will be appreciated by those of skill in theart that the genset may or may not operate as a primary or back-upgenerator and/or may or may not operate in parallel with one or moreother gensets or electric power sources.

FIG. 1 depicts electrical power system 20 of a further embodiment of thepresent application. Electrical power system 20 includes an electricpower generation genset subsystem 22. Genset 22 includes a prime mover22 a in the form of an internal combustion engine 24 and an alternatoror electric power generator 30 to provide a three-phase, AlternatingCurrent (AC), voltage at a target magnitude and frequency. In otherarrangements, power may be supplied as a single phase or in such otherconfiguration as would occur to those skilled in the art.

Engine 24 provides rotational mechanical power to generator 30 withrotary drive mechanism 26. Mechanism 26 can be a direct drive member, adevice that provides a nonunity turn ratio, a torque converter, atransmission, and/or a different form of rotary linkage as would occurto those skilled in the art. In one arrangement, mechanism 26 is in theform of an extension of a crankshaft of engine 24 that serves as a rotorwithin generator 30 and thus the engine and generator have a one-to-oneturning ratio. The depicted form of engine 24 includes one or morereciprocating pistons 23 in corresponding cylinders and is structuredfor Spark Ignition (SI) combustion. Correspondingly, engine 24 utilizesan SI compatible fuel such as natural gas, liquid petroleum gas,molecular hydrogen, a different gaseous fuel; gasoline; or other SIcompatible fuel type. Alternatively, the genset engine can be of aCompression Ignition (CI) type (such as a diesel-fueled engine)utilizing a CI-compatible fuel such as diesel, JP8 or JP5. Fuel may beintroduced through fuel injection. In certain diesel engine embodiments,fuel is injected on a per cylinder basis using direct injection or portinjection—such that there is one fuel injector per cylinder—facilitatingindependent cylinder-by-cylinder fueling control. System 20 includesfuel source 24 a , supplied by conduit 24 b , which is coupled to engine24. Fuel from source 24 a is mixed with air from air intake 25 upstreamof pistons 23 to provide a fuel charge thereto.

In other forms, engine 24, mechanism 26, and/or generator 30 can be ofother types; engine 24 may be alternatively fueled and/or have differentcombustion modes or cycles; and/or a different form of engine-basedprime mover 22 a can be used to provide mechanical power to generator 30as an alternative or addition to engine 24, like a CI engine type, a gasturbine engine type, a two-stroke engine type, among others. Differentforms of prime mover 22 a further include, without limitation, a windturbine, a hydraulic turbine, and/or a steam turbine.

Generator 30 includes excitation field windings 32 operatively coupledto controller 70 to be further described hereinafter. The electric poweroutput of generator 30 is coupled to switchgear 40 to selectively coupleand decouple the generator electric power output to/from the publicutility power grid 46. For arrangements in which system 20 is dedicatedto supply power to grid 46, switchgear 40 typically is in the form ofbreakers for each power line. Alternatively, for a stand-by or back-uppower application of system 20, switchgear 40 would typically include atransfer switch coupled to grid 46 and a local electrical load (notshown). Furthermore, one or more transformers may be provided betweenswitchgear 40 and the connection to grid 46 (not shown). In onenonlimiting implementation, genset 22 includes engine 24 in the form ofa multiple-cylinder, reciprocating piston, gaseous-fueled SI type andgenerator 30 in the form of an alternator with a rotor, which may beprovided on an extension of the engine crankshaft (not shown).

Electrical power system 20 further includes voltage sensors 64 tomonitor the magnitude of voltage output by generator 30 on conductors34. Sensors 64 may be in the form of circuitry that samples a voltagedrop across a known resistance or the like. Electrical power system 20further includes current sensors 62 that monitor magnitude of electriccurrent flow through conductors 34, neutral (N), and ground (GND), inassociation with generator 30. Sensors 62 may be of a standard currenttransformer type or such other variety as would be known to thoseskilled in the art. Sensor 66 is of a standard type that provides asensor signal representing rotational speed of engine 24. In some forms,the sensor signal of sensor 66 is representative of the frequency of theelectric power output of generator 30; however, frequency of theelectric power output can be determined using other techniques. Sensors62, 64, and 66 are converted to a digital form for processing usingstandard techniques. Alternatively or additionally, in otherembodiments, an analog form of sensor signal processing may be used.

Electrical power system 20 further includes controller 70 coupled tosensors 62, 64, and 66. Controller 70 may be provided with generator 30as part of the power generation genset 22 and may be in the form of onecontrolling device for both engine 24 and generator 30 or may be in theform of two or more controlling devices such as a dedicated EngineControl Module (ECM) in communication with a dedicated generator/gensetcontrol module, just to name a few nonlimiting examples. In oneparticular form, engine 24, generator 30, and controller 70 are providedas integrated equipment. Controller 70 includes inputs from currentsensors 62 corresponding to the three phases of the electrical output ofgenerator 30 designated as “3φI,” any detected neutral currentdesignated as “NI,” and any detected electric earth ground currentdesignated as “GNDI.” Sensors 64 provide voltages corresponding to thethree-phase electric output of generator 24 designated as “3φV.” Theengine speed input from sensor 66 is designated as “RPM.” Operation ofengine 24 is regulated by controller 70 in response to signalstherefrom.

Controller 70 includes memory 74. Controller 70 executes operating logicthat defines various control, management, and/or regulation functions.This operating logic may be in the form of dedicated hardware, such as ahardwired state machine, programming instructions, and/or a differentform as would occur to those skilled in the art. Controller 70 may beprovided as a single component or a collection of operatively coupledcomponents; and may be comprised of digital circuitry, analog circuitry,software, or a hybrid combination of any of these types. Controller 70can include multiple processing units arranged to operate independently,in a pipeline processing arrangement, in a parallel processingarrangement, and/or such different arrangement as would occur to thoseskilled in the art. When controller 70 is of a multi-component form, itmay have one or more components remotely located relative to the others.In one embodiment, controller 70 is a programmable microprocessingdevice of a solid-state, integrated circuit type that includes one ormore processing units and memory. In one form, controller 70 can includea computer network interface to facilitate communications using one ormore standard communication protocols. Such an interface may be used toreport system status information, receive sensor/detector inputs,operator input/output, communicate other data used in its operation,perform remote debugging or monitoring of controller 70, and/or toreceive operating logic updates in the form of programming instructionsor the like. It should be appreciated that one or more operator inputcontrols, such as a keyboard, pointer, switches, or the like; and one ormore operator outputs, such as a display, alarm, indicator, or the likecan be included in genset 22 with appropriate interfacing to controller70.

Memory 74 may be comprised of one or more types including but notlimited to semiconductor, magnetic, and/or optical varieties, and/or maybe of a volatile and/or nonvolatile variety. In one form, memory 74stores programming instructions executed by controller 70 to embody atleast a portion of its operating logic. Alternatively or additionally,memory 74 stores data that is manipulated by the operating logic ofcontroller 70. Controller 70 may include signal conditioners,modulators, demodulators, Arithmetic Logic Units (ALUs), CentralProcessing Units (CPUs), oscillators, control clocks, amplifiers,communication ports, delay devices, signal format converters (such asanalog-to-digital and digital-to-analog converters), limiters, clamps,filters, power supplies, and the like as needed to perform variouscontrol, management, and regulation operations described in the presentapplication.

Controller 70 may control/monitor a number of aspects of genset 22operation, such as electrical load change/transience, electronicgovernor control, automatic voltage regulation, regulated short circuitcurrent, engine speed sensing, engine fault monitor,overload/overcurrent fault, neutral current fault, earth ground fault,short circuit fault, automatic synchronization with other AC powersources, permissive paralleling with other generators, parallelingcontrol, over/undervoltage faults, remote metering and control,generator start-up control, output power calculation and display,reverse power fault, real power load sharing control during paralleloperation, reactive power load sharing control during paralleloperation, built-in self-diagnostics, and provision for externaldiagnostics equipment, just to name a few. Two common control functionsare: (1) the regulation of the frequency of the generator outputwaveform typically performed by adjusting engine operation and, (2) theregulation of the voltage and/or electric current produced by generator30.

Having described various structural and relational aspects of system 20and its constituents, various modes of operating system 20 are nextdescribed. These operating modes/processes can be implemented, asapplicable, via the operating logic executed by controller 70 and/orusing such other techniques as would occur to those skilled in the art.

Among the operations that may be performed under the direction ofoperating logic executed by controller 70 is the detection of a lowvoltage condition on the grid 46 that is suitable for LVRT and todistinguish the same from other types of faults and failures. Certainapplications of the present invention are directed to grid 46 having anominally constant AC voltage and frequency, with a three-phase orsingle-phase sinusoidal waveform characteristic. Referring to FIG. 7, anexemplary sinusoidal AC waveform is illustrated in terms of voltagemagnitude versus time to aid in explaining these aspects. Specifically,FIG. 7 depicts a few representative Zero Cross (Z_(C)) events where thepolarity of the voltage magnitude switches between positive andnegative, a representative positive voltage peak (V+), and arepresentative negative voltage peak (V−).

For such applications, in one embodiment an LVRT condition is determinedas a function of two separate, but complementary aspects of the gridvoltage: loss of voltage zero cross and low absolute voltage peakmagnitude between two zero crosses. When the grid voltage is low, butstill present, a “sag” detection module can be employed. In one formthis sag detection module is implemented by a routine that: (a)digitally samples of the voltage signal at a sampling frequency>>thetarget AC frequency and stores the largest absolute peak value sampleduntil a zero cross event occurs, (b) when a zero cross event occurs, thepeak sampled value is compared to a stored threshold value, and (c) ifthe peak sampled value is less than the threshold value a low voltageevent is signaled and otherwise the peak sampled value is discarded andthe routine repeats.

However, if there is a dead short circuit across the grid or other eventthat drives the grid voltage toward zero, it is possible the voltagewill be at or near zero for an extended period and no zero cross eventswill occur. As a result, the sag detection module may continue samplingand never trigger the low voltage event. Accordingly, for certainapplications, detection of LVRT further includes a loss of zero crossdetection module. In one form, this loss of zero cross detection moduleis implemented by a routine that: (a) resets a timer at every zerocross, and (b) if this timer times out without being reset by asubsequent zero cross, a low voltage or no-zero cross fault is signaled.The zero cross loss timer has a time out value selected to be more thana one-half period of the target AC sinusoidal waveform, but less than afull period. In one implementation, a time out value of 0.75 of thetarget sinusoidal waveform period is selected to reject minor variationsin grid frequency, but still detect a dead short circuit quickly enoughfor a timely system response.

Once a low voltage event is detected, controller 70 generates one ormore signals to change spark ignition timing of engine 24 in certainembodiments. For an embodiment having a controller 70 comprised of agenset processor and a dedicated ECM, the genset processor signals theECM to, for example, retard or inhibit the engine timing. Thiscommunication may take place as a high priority Controller Area Network(CAN) bus message; a dedicated hardwired line from an output of thegenset processor to an interrupt input of a processor of the ECM; and/orusing such other techniques as would occur to one skilled in the art.

Upon detecting a transient load situation with controller 70 (such as alow voltage on the power grid or “short circuit” condition) that islikely to result in an undesirable frequency change unless otherwiseaddressed, one inventive approach is to use a rapid retarding of theengine spark timing of a spark ignition (SI) engine to significantlyreduce the engine power. The retarded spark timing significantly delaysthe combustion event and thus the combustion efficiency. In anotherinventive approach utilizing a CI engine in place of an SI engine, thefuel injection timing of a compression ignition (CI) engine is rapidlyretarded to delay the combustion event and reduce combustion efficiency.Alternatively, the CI engine rapidly reduces the amount of fuel beinginjected to reduce engine power without a fuel injection timing change.Changes to the spark event for an SI engine, or the fuel injection eventfor a CI engine, can be made on a cycle-to-cycle basis in a sequentialpattern of some or all cylinders of a multicylinder engine and thereforeit can provide a near instantaneous engine power reduction in responseto a reduction in genset load (such as a drop in grid voltage).

In one embodiment, the low voltage condition triggers retardation ofignition spark timing, direct injection timing, or reduced directinjection fueling relative to nominal using an “all-or-nothing” approach(or so-called “Bang-Bang” algorithm). For instance, subject to thiscondition being true, controller 70 directs a maximum level of retardedspark ignition timing when engine speed “n” exceeds a designated upperthreshold (UT)—appreciating that n is proportional or in one-to-onecorrespondence with the frequency f of the AC voltage and currentwaveforms produced by the generator 30. Once n drops below a designatedlower threshold (LT), controller 70 returns to nominal spark ignitiontiming. Controller 70 thus modulates between maximum retarded sparkignition timing and nominal spark ignition timing based on the enginespeed n during the low voltage condition transient. The selection of thespeed/frequency band (LT through UT) depends on the specific equipmentcharacteristics and desired performance level. In the case of a CIengine type, the controller can direct the retardation of fuel injectiontiming and/or the reduction in the amount of fuel injected.

A complementary or alternative method is to more completely interrupt orinhibit the ignition event in a sequential pattern of some or allcylinders of a multicylinder engine or inhibit ignition in all cylindersentirely during the short transient event, for example. Likewise, in aCI engine embodiment, fuel amount is reduced to zero or fueling isotherwise withheld or skipped. Like the retarded spark timing for an SIengine (or the retarded fuel injection timing or reduced amount of fueldirectly injected for a CI engine) this approach will also produce anear instantaneous response. As the control system adjusts the fuelsystem settings in response to the lower genset load, the spark timingor spark interruptions, or direct injection timing, direct injectioninterruptions, or reduced direct injection fueling, may be adjusted asnecessary to restore a more normal setting.

Still another embodiment is to use the spark timing, spark interruptionand/or direct injection timing to allow for a subsequent rapid increasein the load and corresponding increase in engine power output after atransient low voltage event. For instance, if during this same loaddisruption, the load were to suddenly reappear, the engine speed wouldfall dramatically if fueling changes were made as suggested above.However, by maintaining the previous high fueling state and rapidlyreturning the spark events or direct injection timing to a more normalstate, the ability of the engine to handle the load will be rapidlyrestored. For applications including a turbocharger, it should beappreciated that use of retarded fuel injection or retarded sparkignition can maintain or even increase turbocharger rotational speed bycorrespondingly adjusting exhaust flow and/or temperature, such that theengine does not experience a so-called “turbo lag” upon resumption ofthe load as the turbocharger spools up again. In contrast, standardturbocharger engine systems tend to experience this lag because of therelatively low flow rate and/or temperature of the exhaust under lightload or no load conditions.

Rapid load changes to a genset can cause unacceptable changes to theengine speed if the system is incapable of a sufficient response inmagnitude and duration. Engines that can change the power generated fromeach cylinder on a cycle-to-cycle basis typically have the best chanceof producing an acceptable outcome during these excursions.

Engines for which individual cylinder outputs can be changed on acycle-by-cycle basis or near cycle-by-cycle basis include diesel andport/direct injected SI configurations. Spark ignition engines thatintroduce the fuel upstream of the cylinder (e.g. throttle body orcarbureted) cannot affect this rapid change in load due to the transportdelay through the intake between the fuel injection location and thecylinder. However, carbureting the fuel upstream of a turbocharger iscommon due to the lower cost of fuel system hardware and the ability toinject the fuel at low pressures (e.g. pipeline natural gas). Thedownside for such arrangements can be the aforementioned transportdelay, which leads to poor transient response during rapid load changes.

It should be appreciated that spark timing retard, spark interruption,direct injection timing, fuel injection interruption or reduced injectedfueling can be utilized together or in the alternative to address theload transient. Either technique can change the engine power in adesired fashion in response to a sudden change of load (such as a gridvoltage drop). Spark or direct fuel injection timing alteration (for SIor CI engine-based systems respectively) is capable of rapidly changingthe output of the power per cylinder by changing the timing of thecombustion event and consequently the efficiency of the combustionprocess. For example, a significant reduction in genset load (such as adrop in power grid voltage) can be quickly sensed and the spark or fuelinjection timing retarded as required to prevent a detrimental increasein speed. During this event, the fuel still burns in the cylinder, butthe work extracted during the expansion process can be controllablydiminished. Spark interruption or fuel injection interruption isaccomplished by eliminating all spark or fuel injection events for ashort time period or by sequentially interrupting cylinders as necessaryto quickly reduce engine power. Any undesirable accumulation of unburnedfuel in the exhaust with spark ignition (SI) engines can be limited byusing a short duration of interruption, by skip firing in adjacentcylinders, and/or through various aftertreatment techniques.

Furthermore, with spark ignition (SI) engines if the load is rapidlyfluctuating due, for example, to the rapid opening and closing ofbreakers on the system or grid, then the fueling can be left at a highersetting during the event; while at the same time, changes to the sparkevents (timing and/or interruption) can be immediately switched in andout to minimize undesirable changes in engine speed. With the previousfueling still in place, the rapid return of normal spark settings willresult in a rapid increase in engine load as there is no lag time forfueling changes to be seen as the air/fuel mixture ratio being added tothe engine and entrained in the intake has been left the same during theevent. If the load change lasts longer than a predefined period of time,the control system may return the control of upstream fueling and sparkevents to their normal settings; returning the spark events to a normaltiming setting and allowing the fueling to be reduced to reduce poweroutput for what has proven to be a non-transient event. Fuel injectiontiming alteration or injected fuel amount reduction can be utilized withcompression ignition (CI) engines to rapidly reduce and restore power asload returns.

During these transient events, controller 70 monitors frequencydeviation and duration to determine total phase angle deviation. Sparkignition or fuel injection, controllable for each engine cylinder, canthen be utilized to control engine speed/frequency to adjust the phaseangle deviation back to the nominal value required. Fueling changes, ifany, would also be determined by controller 70.

During an event where the voltage is forced to zero or near zero,controller 70 can generate a virtual voltage zero-crossing based on thelast measured zero-cross, which may be useful when operating insynchronization with another large power source. This virtual zero-crosscan be utilized as a timing reference signal for phase angleresynchronization. Alternately, the zero-cross reference signal could besupplied externally based on information transmitted by the other powersource.

In some embodiments, it should be appreciated that aspects of standardgenset load and speed/frequency controls may be in operation duringtransient events; however, these standard controls typically aresubordinate to the transient technique(s) applied as described aboveuntil the transient event is over. In still another form, the spark orfuel injection control loop could be integrated into a more traditionalcontrol architecture in certain embodiments.

Some or all of these techniques can be applied in a parallel generatorsystem, such as electrical system 320 illustrated in FIG. 2; where likereference numerals refer to like features previously described. System320 includes a number of electric power generation subsystems 322 eachhaving electric output sensors of the type previously described (notshown), an engine or other prime mover (not shown), generator 330, andcontroller 70, respectively. Any of the generators 330 set forth insystem 320 may be any of the types previously described, such asgenerator 30, or of a different type. Subsystems 322 are arranged forselective parallel operation to provide a corresponding parallel powersource 326. Source 326 also includes power bus 332, generator feederconductors, 334, and power breaker/switches 340, respectively. Eachgenerator 330 of system 320 can be connected and disconnectedselectively to power bus 332 by corresponding feeder conductors 334through a respective power breaker/switch 340. Power bus 332 can becoupled to local power bus 352 by breaker/switch 350. Source 326 is thenselectively connected to grid 46 by the closure of power breaker/switch360 connected to power bus 352.

A further embodiment utilizes a series of resistors and switches toabsorb extra energy during an LVRT event, maintaining relativelyconstant voltage upstream from the device. One example of thisembodiment is illustrated as system 420 in FIG. 3; where like referencenumerals refer to like features previously described. Theswitching/resistor device 422 also assists in maintaining engine speedto improve the engine's ability to maintain synchronization by absorbingthe excess power that the grid would otherwise be consuming.

The switching speed determines the rate of controllability. Mechanicalswitches can function on the order of 10 ms or slower. Though mechanicalswitches would provide some benefits, faster switching times would bedesired in certain implementations, which may turn to solid-stateswitches having sub-ms switching times as an alternative. To the extentsolid-state switches are considered too costly, gas ionization switches,which are also faster than mechanical switches may be utilized, and/orsuch other switch types as would occur to those skilled in the art.

For a typical implementation, the resistor element(s) should be sized tohandle 2-20 seconds of use without causing damage such as melting orbecoming disfigured from the resistive heating without active cooling.Iron is one nonlimiting example of a common/low-cost material that couldprovide the conductivity, specific heat, and mass for this application.For example, 50 kg of iron could withstand 1 MW of resistive heating for5 seconds and increase in temperature by less than 250 K, which wouldnot cause a phase change in the material. After some set amount of timethe device would completely decouple the grid from the generator if theundervoltage persists. The FIG. 3 illustration is just one possibleexample of a resistor/switch network device 422. Voltage controlresolution is (Full Voltage)/2^(n). In this seven (7) resistor example,the resolution is 1/128=0.78%. As shown in FIG. 3, the bypass breakercan provide a minimum resistance pathway P1 during normal operation, andwould trip at the beginning of the disturbance, giving theswitch/resistor device 422 along pathway P2 control over resistanceuntil the grid stabilized or it is determined that the generator 30should be decoupled. Typically, a device 422 would be applied to eachphase of the generator. FIG. 4 depicts a graph of voltage and resistanceduring an estimated LVRT event.

The LVRT approach of system 420 can be combined with any of thepreviously described techniques to address load transients, such asretarded spark timing, skip-firing, spark interruption, fuel injectiontiming, reduce injected fuel, direct injection interruption (a specificform of injected fuel reduction) and associated variants and controls.Further, it may be implemented in arrangements with or without parallelgensets, and in still other embodiments, may additionally oralternatively include one or more other impedance-altering services suchas inductors or capacitors, with or without resistive elements such asthose shown; and/or network device 422 may be altogether absent.

In a further embodiment that may be used in concert with or in lieu ofspark ignition timing control, fuel injection timing control, and/or aresistive/switching network; the system uses the alternator/generatorfield to generate a short circuit current and load the engine 24 withtorque when the grid load drops. The additional load on the engine mayreduce engine acceleration during the voltage drop period. When thevoltage drop ends and the grid load returns, the phase differencebetween the genset 22 and the grid 46 may not be out of synch enough forpole slipping. In one form, this field is controlled by the voltageapplied to the excitation windings 32. This voltage control drives thealternator field current to a maximum value to generate a large shortcircuit current (and power) to help balance engine torque to alternatorelectromagnetic torque. This torque balance keeps the engine speed fromaccelerating, and going out of phase relative to the grid voltage.

In one particular embodiment, controller 70 directs the alteration ofspark ignition of engine 24 and adjustment of the alternator field inresponse to a low voltage condition. In a further refinement of thisembodiment, the alteration of spark ignition includes retarding sparkignition timing and/or the adjustment to the alternator field includesincreasing it to a full field state. For a CI engine, injected fuelamount reduction (including withholding fuel or inhibition—that isreducing the amount to zero) and/or fuel injection retardation may beutilized. In many applications, this combination of engine sparkretard/alternator field increase(SI engines) or engine fuel injectionmodification/alternator field increase (CI engines) provides a desirableway to balance the engine and alternator torque during one of these lowvoltage events. The system response is as previously disclosed; namelyto have the engine control module (ECM) retard the engine ignitiontiming for an SI engine (or retard/reduce fuel injection for a CIengine) to the minimum desired value, while simultaneously the gensetvoltage control drives the alternator field current is to a maximumvalue to generate a large short circuit current (and power) to helpbalance engine torque to alternator electromagnetic torque. This torquebalance keeps the engine speed from accelerating, and going out of phaserelative to the grid voltage.

Even so, in still other embodiments, a better balance may be desired.Accordingly, such other embodiments may add other features to the enginespark retard/alternator field increase combination for an SI engineembodiment (or fuel injection modification/alternator field increasecombination for a CI engine embodiment) to improve the balance. Itshould be appreciated that the engine spark retard/alternator fieldincrease for an SI engine application (or fuel injectionmodification/alternator field increase for a CI engine application) canbetter enable the addition of such features compared to standardschemes. By way of nonlimiting example, if a brake of some type is usedwith such combination to absorb excess torque, the sizing/specificationsof such a brake can be significantly reduced. In another example, ifinertia is added to the system in the form of a flywheel, or largeralternator, the extra inertia required can be significantly reduced whenadded to the combination. Furthermore, more than one of these featurescan be added to this combination. Such features further include: (a) amechanical brake, (b) an exhaust brake such as an exhaust brake of thejake-brake and/or turbocharger-actuated type to name a couple ofexamples, (c) increased system inertia through sizing of gensetcomponents and additional flywheels or the like, and/or (d) switchableimpedance to change alternator loading as described in connection withFIG. 3. Alternatively or additionally, the engine sparkretard/alternator field increase combination provides a basis formodification of standard components to better take advantage of thecombination. For example, one could modify the alternator to go to fullfield faster and/or to produce more short circuit current (and sooner),which could include: increasing exciter voltage to decrease exciter timeconstants, removing the on-alternator exciter and using slip rings witha separate energy source to charge the field more quickly, and/oraltering other alternator thermal (and electrical) time constants andimpedances to support the increase in short circuit currents in bothduration and amplitude. In another example on the engine side, it couldbe modified to improve the robustness of exhaust manifolds or exhaustsystems in case of exhaust over pressure events are triggered by sparkinhibition or the like. Referring to FIG. 5, the graph provides thestandards established for low voltage ride through capabilities ofvarious jurisdictions. For nominal voltage levels and durations that arein Area A near the bottom and to the right of line 510, disconnectionfrom the grid may be allowed. The system of an embodiment of the presentinvention performs to maintain connection without damage to thecomponents when functioning above and to the left of Area A. When theconditions of the LVRT are within Area B (below line 520 and above line510), the system may operate with modified spark timing and an increasedalternator field to slow the engine and maintain synchronization withthe grid.

FIG. 6 shows another graph relating to another embodiment where thesystem performs various features of the present invention to maintaingrid connectivity during a LVRT event with like references relating tolike features. For nominal voltage levels and durations that are in AreaB, the system may include features such as spark timing modification andan increased alternator field. In Area C above line 620 and below line630, the system may include features such as a resistive circuit inaddition to spark timing modification and an increased alternator field.The system may use these features to keep the genset speed andsynchronization within acceptable limits.

In still other embodiments two or more of: a spark ignition timingadjustment for an SI engine, (or fuel injection timing adjustment and/orinjected fuel reduction for a CI engine on a per cylinder basis),generator field adjustment, and resistive loading are used incombination. In some implementations, it has been surprisinglydiscovered that spark ignition retardation and increasing the generatorfield voltage is desirable.

In further embodiments, one or more of spark ignition timing adjustmentfor an SI engine (or adjustment of fuel injection timing and/or areduced amount of injected fuel controllable at the cylinder level for aCI engine), generator field adjustment, and resistive loading are usedin combination with one or more other techniques, such as the inertiaincrease provided by a flywheel on a power shaft of the genset, anotherwise over-sized generator or alternator, a brake of some sort, likean engine exhaust brake, or the like.

Additionally or alternatively, the alternator/generator could bemodified to go to full field faster, and to produce more short circuitcurrent (and sooner). Such things might include increasing excitervoltage to decrease exciter time constants, removing the onalternator/generator exciter and using slip rings with a separate energysource to charge the field quicker. Altering other alternator thermal(and electrical) time constants and impedances to support the increasein short circuit currents in both duration and amplitude and the like.

Many further embodiments of the present application are envisioned.Among the inventions desired to be protected are:

A method, comprising: providing electric power to a utility grid, whichincludes driving an electric power generator coupled to the grid with aspark-ignited internal combustion engine; detecting a change inelectrical loading of the generator; in response to the change, changingspark ignition of the engine to adjust power provided by the engine. Inone further form of this method, the changing of spark ignition includesretarding spark timing. In another form of this method, the changing ofspark ignition includes interrupting the spark ignition.

An inventive apparatus comprising: a genset including an electric powergenerator structured for coupling to an electric power grid, aspark-ignited internal combustion engine to drive the generator, acontroller structured to regulate operation of the genset; wherein thecontroller executes operating logic to detect a change in electricalloading of the generator and in response to the change, to adjust sparkignition of the engine. The adjustment of spark ignition may includeretarding spark timing and/or interrupting the spark ignition ininventive variations of the apparatus.

A further inventive apparatus comprising: a genset including an electricpower generator, a spark-ignited internal combustion engine to drive thegenerator, means for providing electric power generated from thegenerator to a utility grid, means for detecting a change in electricalloading of the generator, and means for adjusting spark ignition of theengine in response to the change.

In further inventive forms, the adjusting means includes means forretarding spark timing and/or means for interrupting the spark ignition.

In another embodiment, an inventive method comprises: providing electricpower to a utility grid, which includes driving an electric powergenerator coupled to the grid with an internal combustion engine;detecting a change to a low voltage condition on the grid; in responseto the low voltage condition, routing electric current output by thegenerator from a less electrically resistive pathway to a moreelectrically resistive pathway to absorb excess energy, and returningthe electric current output to the less electrically resistive pathwayafter the low voltage condition ceases. Further inventive methodvariations include: providing a series of resistors and switches toadjust electrical resistance along the more electrically resistivepathway, providing a switch to electrically open or close the lesselectrically resistive pathway, providing an electrical load between thegenerator and the pathways, maintaining engine speed and/orsynchronization with the grid, and/or addressing an electrical loadtransient by adjusting spark ignition in response to detection of suchtransient.

Still another inventive apparatus comprises: a genset including anelectric power generator structured for coupling to an electric powergrid, a spark-ignited internal combustion engine to drive the generator,a controller structured to regulate operation of the genset; wherein thecontroller executes operating logic to detect a change in electricalloading of the generator and in response to the change, to adjust sparkignition of the engine. The adjustment of spark ignition may includeretarding spark timing and/or interrupting the spark ignition in variousother inventive forms.

A further inventive apparatus comprises: a genset including an electricpower generator, an engine to drive the generator, means for detecting achange to a low voltage condition on the grid; in response to the lowvoltage condition, means for routing electric current output by thegenerator from a less electrically resistive pathway to a moreelectrically resistive pathway to absorb excess energy; and means forreturning the electric current output to the less electrically resistivepathway after the low voltage condition ceases. Additionally, inventiveapparatus variations thereof include means for providing a series ofresistors and switches to adjust electrical resistance along the moreelectrically resistive pathway, means for providing a switch toelectrically open or close the less electrically resistive pathway,means for providing an electrical load between the generator and thepathways, means for maintaining engine speed and/or synchronization withthe grid, and/or means for addressing an electrical load transient byadjusting spark ignition in response to detection of such transient.

Yet another inventive apparatus comprises: a genset including anelectric power generator structured to provide electric power to a powerutility grid, an engine to drive the generator, and circuitryselectively coupling the generator to the grid including a firstelectrical pathway and a second electrical pathway in parallel with thefirst electrical pathway, the first pathway being less electricallyresistive than the second pathway, and a controller structured toexecute operating logic to detect a low voltage condition on the gridand route electric current from the generator from the first pathway tothe second pathway to absorb excess energy and to adjust resistance ofthe second pathway. Additional inventive features thereof include meansfor rerouting the current to flow through the first path after the lowvoltage condition ceases, and/or wherein the second pathway includes anumber of switches and resistors to provide a switch-adjustable variableresistance, and/or wherein the first pathway includes a switch in theform of a circuit breaker.

In another embodiment, a method includes: providing electric power to autility grid, which includes driving a field-adjustable alternatorcoupled to the grid with a spark-ignited internal combustion engine;detecting a low voltage condition of the utility grid; and, in responseto the low voltage condition changing spark ignition of the engine andadjusting a field produced by the alternator.

Also embodiments of the present application include an apparatuscomprising: an electric power generator structured for coupling to anelectric power grid; a spark-ignited internal combustion engine to drivethe generator; a sensing device; and a controller responsive to thesensing device to regulate operation of the generator and the engine.The controller is structured to determine a low voltage condition of theelectric power grid and in response to the low voltage condition toprovide one or more output signals to change spark ignition of theengine and adjust a field of the generator.

A further embodiment includes an apparatus, comprising: a gensetincluding an adjustable-field alternator and a spark-ignited internalcombustion engine to drive the alternator. The genset is operable tointerface with a public utility grid and includes a controller. Thecontroller includes: means for determining a low voltage condition ofthe utility grid; and means for responding to the low voltage conditionincluding means for increasing engine load and means for reducing enginespeed.

Still a further embodiment is directed to a technique, comprising:driving an electric power generator with a spark-ignited internalcombustion engine to provide electric power to a utility grid;determining a low voltage condition of the utility grid;

and in response to the low voltage condition, changing spark ignition ofthe engine to control engine speed.

Yet a further embodiment is directed to a genset. The genset includes:an electric power generator structured for coupling to an electric powergrid; a sensing device; a spark-ignited internal combustion engine todrive the generator; and a controller structured to regulate operationof the genset. The controller is responsive to the sensing device todetermine a low voltage condition of the electric power grid and provideone or more output signals to adjust spark ignition of the engine inresponse to the low voltage condition.

In another embodiment, a method includes: providing electric power to autility grid, which includes driving an adjustable field electric powergenerator coupled to the grid with an internal combustion engine;detecting a low voltage condition of the utility grid; and in responseto the condition, increasing a field of the generator to increase torqueon the generator.

A further embodiment is directed to a genset including: an electricpower generator structured for coupling to an electric power grid; asensing device; a spark-ignited internal combustion engine to drive thegenerator; and a controller structured to regulate operation of thegenset. The controller is responsive to the sensing device to determinea low voltage condition of the electric power grid and in response tothe condition to provide one or more output signals to increase anadjustable field of the generator.

In another embodiment, a method includes: providing electric power to autility grid, which includes driving an electric power generator coupledto the grid with a compression-ignited internal combustion engine;detecting a change in electrical loading of the generator; in responseto the change, changing direct injection of fuel to the engine to adjustpower provided by the engine. In one further form of this method, thechanging of compression ignition includes retarding direct fuelinjection timing. In another form of this method, the changing ofcompression ignition includes interrupting the direct fuel injection. Ina further form of this method, the changing of compression ignitionincludes changing the amount of fuel injected in the direct fuelinjection.

A further inventive apparatus comprises: a genset including an electricpower generator structured for coupling to an electric power grid, adirect fuel injection compression-ignition internal combustion engine todrive the generator, a controller structured to regulate operation ofthe genset; wherein the controller executes operating logic to detect achange in electrical loading of the generator and in response to thechange, to adjust compression ignition of the engine. The adjustment ofcompression ignition may include retarding direct fuel injection timing,reducing direct fuel injection fuel amount and/or interrupting thedirect fuel injection in inventive variations of the apparatus.

Still another inventive apparatus comprises: a genset including anelectric power generator, a direct fuel injection compression-ignitioninternal combustion engine to drive the generator, means for providingelectric power generated from the generator to a utility grid, means fordetecting a change in electrical loading of the generator, and means foradjusting compression ignition of the engine in response to the change.In further inventive forms, the adjusting means includes means forretarding direct fuel injection timing, reducing direct fuel injectionfuel amounts and/or interrupting the direct fuel injection.

Any theory, mechanism of operation, proof, or finding stated herein ismeant to further enhance understanding of the present invention and isnot intended to make the present invention in any way dependent uponsuch theory, mechanism of operation, proof, or finding. It should beunderstood that while the use of the word preferable, preferably orpreferred in the description above indicates that the feature sodescribed may be more desirable, it nonetheless may not be necessary andembodiments lacking the same may be contemplated as within the scope ofthe invention, that scope being defined by the claims that follow. Inreading the claims it is intended that when words such as “a,” “an,” “atleast one,” “at least a portion” are used there is no intention to limitthe claim to only one item unless specifically stated to the contrary inthe claim. Further, when the language “at least a portion” and/or “aportion” is used the item may include a portion and/or the entire itemunless specifically stated to the contrary. While the invention has beenillustrated and described in detail in the drawings and foregoingdescription, the same is to be considered as illustrative and notrestrictive in character, it being understood that only the selectedembodiments have been shown and described and that all changes,modifications and equivalents that come within the spirit of theinvention as defined herein are desired to be protected.

What is claimed:
 1. A method, comprising: providing electric power to autility grid, which includes driving a field-adjustable alternatorcoupled to the grid with a spark-ignited internal combustion engine;detecting a low voltage condition of the utility grid; in response tothe low voltage condition: changing spark ignition of the engine, thechanging of the spark ignition including retarding a timing of the sparkignition so as to preserve synchronization with the utility grid; andadjusting a field produced by the alternator, wherein the retarding thetiming of the spark ignition comprises modulating the timing between amaximum retarded timing and a nominal timing based on a speed of theengine during the low voltage condition.
 2. The method of claim 1,wherein the adjusting of the field includes changing to a full fieldstate of the alternator.
 3. The method of claim 1, which furtherincludes braking at least one of the alternator and the engine inresponse to the low voltage condition.
 4. The method of claim 1, whichfurther includes switching in an impedance circuit to increaseelectrical load on the alternator in response to the low voltagecondition.
 5. The method of claim 1, wherein the changing of the sparkignition includes retarding spark ignition timing.
 6. The method ofclaim 1, wherein the adjusting of the field includes adjusting to a fullfield state in response to a field control voltage.
 7. The method ofclaim 1, which includes: operating the alternator and the engine as agenset regulated with a controller; performing the changing of the sparkignition timing and the adjusting of the field in accordance withoperating instructions executed with the controller; performing thedetecting of the low voltage condition by sensing voltage with one ormore sensors; and fueling the engine with a gaseous type of fuel.
 8. Anapparatus comprising: an electric power generator configured to coupleto an electric power grid; a spark-ignited internal combustion engine todrive the generator; a sensing device; and a controller responsive tothe sensing device to regulate operation of the generator and theengine, the controller being configured: to determine a low voltagecondition of the electric power grid, and in response to the low voltagecondition, to provide one or more output signals to change sparkignition of the engine and adjust a field of the generator, the changingof the spark ignition including retarding a timing of the spark ignitionso as to reduce power output and preserve synchronization with theutility grid, wherein the retarding the timing of the spark ignitioncomprises modulating the timing between a maximum retarded timing and anominal timing based on a speed of the engine during the low voltagecondition.
 9. The apparatus of claim 8, wherein the controller isconfigured to execute programming operable to adjust the field byincreasing to a full field state of the generator.
 10. The apparatus ofclaim 9, wherein the controller is configured to generate the one ormore output signals to change the spark ignition by retarding sparkignition timing of the engine.
 11. The apparatus of claim 10, whereinthe generator, the engine, the sensing device, and the controller areprovided as a genset, and the controller includes an engine controlmodule and one or more other control devices.
 12. The apparatus of claim11, wherein the engine is of a multiple cylinder, reciprocating pistontype.
 13. The apparatus of claim 12, further comprising a fuel sourcecontaining a gaseous fuel for the engine.
 14. A method, comprising:providing electric power to a utility grid, which includes driving afield-adjustable alternator coupled to the grid with a direct injectioncompression-ignition internal combustion engine with fuel injection;detecting a low voltage condition of the utility grid; in response tothe low voltage condition: changing ignition of the engine by alteringthe fuel injection, the altering of the fuel injection includingretarding a timing of the fuel injection so as to reduce engine poweroutput and preserve synchronization with the utility grid; and adjustinga field produced by the alternator, wherein the fuel injection isaltered when a speed of the engine exceeds an upper threshold, andwherein the fuel injection is restored to an unaltered state once thespeed drops below a lower threshold.
 15. The method of claim 14, whereinthe adjusting of the field includes changing to a full field state ofthe alternator.
 16. The method of claim 14, wherein the changing of theignition includes at least one of retarding timing of the fuel injectionand reducing an amount of injected fuel.
 17. The method of claim 16,wherein the reducing of the amount of injected fuel includes withholdingfuel from a cylinder of the engine.
 18. An apparatus comprising: anelectric power generator configured to couple to an electric power grid;a compression ignition internal combustion engine to drive thegenerator, the engine including one or more cylinders with fuelinjection; a sensing device; and a controller responsive to the sensingdevice to regulate operation of the generator and the engine, thecontroller being configured: to determine a low voltage condition of theelectric power grid, and in response to the low voltage condition, toprovide one or more output signals to change the fuel injection to alterengine ignition and adjust a field of the generator, the changing of thefuel injection including one or more of halting injection, reducing anamount of injected fuel, and retarding injection timing on one or morecylinders of the engine so as to reduce engine power output and preservesynchronization with the electric power grid, wherein the fuel injectionis changed when a speed of the engine exceeds an upper threshold, andrestored to an unaltered state once the speed drops below a lowerthreshold.
 19. The apparatus of claim 18, wherein the controller isconfigured to execute programming operable to provide the change to thefuel injection by retarding the fuel injection and adjust the field byincreasing to a full field state of the generator.
 20. The method ofclaim 14, which further includes braking at least one of the alternatorand the engine in response to the low voltage condition, wherein thebraking includes applying an exhaust brake.